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Abstract

We describe a fast mesh-based Monte Carlo (MC) photon migration algorithm for static and time-resolved imaging in 3D complex media. Compared with previous works using voxel-based media discretization, a mesh-based approach can be more accurate in modeling targets with curved boundaries or locally refined structures. We implement an efficient ray-tracing technique using Plücker Coordinates. The Barycentric coordinates computed from Plücker-formed ray-tracing enables us to use linear Lagrange basis functions to model both media properties and fluence distribution, leading to further improvement in accuracy. The Plücker-coordinate ray-polygon intersection test can be extended to hexahedral or high-order elements. Excellent agreement is found when comparing mesh-based MC with the analytical diffusion model and 3D voxel-based MC code in both homogeneous and heterogeneous cases. Realistic time-resolved imaging results are observed for a complex human brain anatomy using mesh-based MC. We also include multi-threading support in the software and will port it to a graphics processing unit platform in the near future.

Validations of MMCM in heterogeneous media. We show the mesh cross-cut-views and the fluence contour plots (with 10db spacing) of two mesh configurations: (a)-(b) a high-density uniform mesh and (c)-(d) a mesh with higher density at the surface of the spherical inclusion and near source.

Tables (2)

Table 2 Optical parameters in various brain tissue types for the human brain atlas simulation. The properties for scalp/skull and cerebro-spinal fluid (CSF) are based on [11] and those for gray and white matters are based on [40] at 630 nm.

Metrics

Table 1

Memory utility and speed comparisons for MMCM and MCX for a heterogeneous simulation.

Nodes

Elements

Memory for mesh data (MB)

Memory for each time-gate (MB)

Speed (in photon/ms) vs. threads*

MMCM Mesh 1

63820

375753

41.3

0.240

5.6 (1), 10.6 (2), 21.5(4)

MMCM Mesh 2

20717

124992

13.7

0.079

5.6 (1), 10.4 (2), 21.2(4)

MCX

60x60x60

-

0.82

0.820

~6700 (thread#>40000)

Table 2

Optical parameters in various brain tissue types for the human brain atlas simulation. The properties for scalp/skull and cerebro-spinal fluid (CSF) are based on [11] and those for gray and white matters are based on [40] at 630 nm.

Tissue types

μa (mm−1)

μs (mm−1)

Anisotropy (g)

Refract. Index (n)

Scalp & skull

0.019

7.8

0.89

1.37

CSF

0.004

0.009

0.89

1.37

Gray-matter

0.02

9.0

0.89

1.37

White-matter

0.08

40.9

0.84

1.37

Tables (2)

Table 1

Memory utility and speed comparisons for MMCM and MCX for a heterogeneous simulation.

Nodes

Elements

Memory for mesh data (MB)

Memory for each time-gate (MB)

Speed (in photon/ms) vs. threads*

MMCM Mesh 1

63820

375753

41.3

0.240

5.6 (1), 10.6 (2), 21.5(4)

MMCM Mesh 2

20717

124992

13.7

0.079

5.6 (1), 10.4 (2), 21.2(4)

MCX

60x60x60

-

0.82

0.820

~6700 (thread#>40000)

Table 2

Optical parameters in various brain tissue types for the human brain atlas simulation. The properties for scalp/skull and cerebro-spinal fluid (CSF) are based on [11] and those for gray and white matters are based on [40] at 630 nm.